川西致密含气砂岩的粘土矿物与潜在地层损害

为了阐明致密含气砂岩储层的损害机理，进而为制订保护气层技术措施提供依据，研究了川西典型气田侏罗系—上三叠统致密砂岩储层中的粘土矿物，采用薄片、ＸＲＤ、ＳＥＭ方法分析了粘土矿物含量、类型、产状和微结构，并讨论了纵向演变规律。研究指出粘土矿物含量随深度增加而降低；粘土类型为高岭石、绿泥石、伊利石、蒙皂石、绿／蒙间层和伊／蒙间层；主要演化路径有蒙皂石→绿／蒙间层→绿泥石、蒙皂石→伊／蒙间层→伊利石、高岭石→伊利石。常见七种粘土微结构类型，随埋深增加微结构稳定性提高。研究还表明粘土自身的敏感性及因粘土的存在而形成的储层致密性是储层易被损害的根本原因，防止致密储层损害，首要工作是有效地解决粘土矿物问题。但仅就防止粘土损害而言，气体类工作流体具有一定程度的优越性。

CLAY MINERALS AND POTENTIAL FORMATION DAMAGE OF TIGHT GAS-BEARING SANDSTONE IN WESTERN SICHUAN BASIN

In order to illustrate formation damage mechanism of tight gas-bearing sandstone and work out a protection scheme during drilling and completion, clay minerals from Jurassic to Upper Triassic sandstone in representative gas fields were studied. Thin section, XRD, and SEM experimental methods were used to analyze the content, type, occurrence and microstructure of the minerals. The study indicates those clay content decreases with increased depth. There are kaolinite, chlorite, illite, smectite, interlayered smectite/chlorite and smectite/illite. Diagenitic history of the minerals is as follows: smectite (interlayered smectite/chlorite (chlorite, smectite(interlayered smectite/illite(I, and kaolinite(iillite. Seven types of clay microstructure are recognized and the stability of clay microstructure increases with depth. The study also shows that clay sensitivities and reservoir tightness, which is resulted from the existence of clays, are the essential factors to cause formation damage. In prevention of formation damage, the most important is to solve the clay problems. Compared with water or oil based working fluids, gas based fluids are superior for damage prevention from clays.